Associating and connecting wireless mobile devices is often a cumbersome process. For instance, transferring a file from a phone using Bluetooth involves a pairing process in which the name of the target device must be known or recognized by the user, further navigation of a number of dialog boxes, and possibly the entry of passwords by the respective user. Part of the difficulty of this process lies in the lack of physical grounding during the connection process—for example, physical feedback plays no role in establishing or breaking the connection. Unlike wired connections, wireless connections have no obvious physical representation in the real world.
Previous systems have explored detecting synchronous events such as touching or bumping devices together or pressing the same key simultaneously as ways of associating two wireless devices in a physically-grounded manner. This approach not only restores some of the tangible feedback of establishing a wired connection, but also allows appropriately equipped devices to find each other automatically. For example, two devices that are equipped with accelerometers may associate based on the observation that “bump” events were recorded at nearly the same point in time. That such a co-occurrence in time may happen accidentally is thought to be unlikely, particularly when near-field wireless communication techniques such as Bluetooth are used. Other systems have demonstrated techniques to connect a mobile device to a large display by having the display present a randomly chosen key which the user then enters on the mobile device. Since the key is only visible to the user as they are viewing a display, the display system has some guarantee that it is connected to the correct device. This key can take the form of an alphanumeric string to be entered on a device keypad, a sequence of motions that are then matched by an accelerometer-equipped device, or a visual pattern shown on the display which is then captured and decoded by camera phone, for example.
Established RFID technologies and upcoming near field communication (NFC) techniques can support device association if the device is equipped with the appropriate radio frequency (RF) tags. Typically this will entail the use of short range (0 to 3 inches) RF identification (RFID) readers which require the placement of the tagged device on a small reading surface. Longer range RFID readers, on the other hand, present the opposite problem: as a user it is difficult to judge whether a given tag is within reading range. This uncertainty can lead to unintended connections and/or raises privacy and security concerns.